The present invention relates to a touch panel that detects the coordinates of an input point from a change in resistance due to a pressing force applied to the input point, and a liquid crystal display device including such a touch panel.
Liquid crystal-display devices used as display means for personal computers and monitors of other apparatuses produce a display in the following manner. An image generated on a liquid crystal panel is illuminated by light, and the light carrying the image is transmitted or reflected toward the display plane so as to be visible to a viewer.
More specifically, this type of liquid crystal display device uses a liquid crystal panel including a pair of substrates, each having pixel selection electrodes and the like mounted thereon. The substrates are bonded together with a liquid crystal layer sandwiched therebetween. An image is generated by changing the orientation state of the liquid crystal molecules in a selected pixel region. The generated image is not intrinsically visible. Therefore, the liquid crystal panel is illuminated by an external light so that the transmitted or reflected tight carrying the image is observed by a viewer.
In recent years, information terminals having touch panels have been broadly used, where the above type of liquid crystal display device is used as a display means and a touch panel is formed on the display screen for allowing various types of information to be input via the display screen.
Touch panels come in various types depending on the principle of operation thereof Among them the most popular is a type that detects the coordinates of an input point from changes in the amount of resistance, called an analog resistor type.
The analog resistor type touch panel includes an input-side substrate made of a transparent soft film and a substrate made of a transparent hard plate, preferably a glass plate. Resistor films are formed on the opposing surfaces of the two transparent substrates. The two resistor films come into contact with each other by application of an external pressing force to a point on the input-side substrate. Two-dimensional coordinate values are detected from resistance values between the resistor films and output terminals.
FIG. 10 is a schematic illustration of the construction of a touch panel equipped liquid crystal display device, where a touch panel 4 is formed on a liquid crystal panel 1. In the illustrated liquid crystal display device, a light guide plate 2 constituting an auxiliary light source device 3 is provided between the liquid crystal panel 1 and the touch panel 4. A construction excluding the auxiliary light source device 3 has also been commercialized. The auxiliary light source device 3 includes a lamp 3A and a lamp reflection sheet 3B.
FIG. 11 is an exploded perspective view illustrating the construction of a conventional analog resistor type touch panel. The touch panel includes two transparent substrates. An upper substrate 4A is a soft film preferably made of polyethylene terephthatate (PET). A resistor film 11 preferably made of indium tin oxide (ITO) is formed on the entire inner surface of the upper substrate 4A. A lower substrate 4B is a hard plate preferably made of glass. A resistor film 22 preferably made of ITO is formed on the entire inner surface of the tower substrate 4B.
Interconnections 35 are formed on two opposing sides of the resistor film 11 of the upper substrate 4A along the edges thereof, and are electrically connected with the resistor film 11. The interconnections 35 have respective terminals at an interface 36 for communication with an external circuit. Connectors 33 and 34 for connection with the lower substrate are formed on the other two opposing sides of the resistor film 11 along the edges thereof, and are electrically isolated from the resistor film 11. The connectors 33 and 34 have respective terminals at the interface 36.
Connectors 43 and 44 for connection with the upper substrate are formed at positions of the resistor film 22 of the lower substrate 4B corresponding to the connectors 33 and 34. Once the upper and lower substrates 4A and 4B are bonded together, connection points T1 and T3 of the connectors 33 and 34 are electrically connected with connection points T2 and T4 of the connectors 43 and 44, respectively, via a conductive material, preferably silver paste. The connectors 33, 34, 43, and 44 are preferably made of the same material as the resistor films in consideration of the ease of the fabrication process. It is needless to mention that the connectors may be made of a material different from that of the resistor films. Thus, the resistor films 11 and 22 formed on the upper and lower substrates constitute a two-dimensional coordinate system, and the coordinates (x, y) (x: x-coordinate value, y: y-coordinate value) of a pressing point (input point) are detected with an external circuit.
The above conventional touch panel has the following problems. Since the resistor films 11 and 22 are solidly formed on the entire surfaces of the upper and lower substrates, the resistance values for detecting the position of the information input point are two-dimensional parameters for the solid resistor films extending between the connectors 33 and 34 and the connectors 43 and 44. Such parameters vary depending on the position of the input point on the resistor films, thereby lowering the linearity.
As a result, the level of detection of the input point becomes degraded, which may cause an input detection error or a deviation (calibration error) between the input point and the display position on a liquid crystal panel mounted on the back of the touch panel. An external circuit (CPU) performs the function of correcting the position. Nevertheless, a detection failure (input failure) is likely to arise, putting this error beyond the ability of function to correct. This causes a lowering in reliability.
Another problem is as follows. The connectors with the opposing substrate are formed on the periphery of one of the substrates (upper substrate in the construction of FIG. 11). This reduces the area of the effective input region and thus makes it difficult to realize so-called narrow framing. In addition, moisture may enter the inside between the substrates from the bonded edges, causing deterioration in the electrical characteristics of the resistor films and the connectors and thereby causing a variation in resistance value. This makes resistance management difficult.
An object of the present invention is to provide a highly reliable touch panel which is free from the occurrence of an input error and input failure, and a liquid crystal display device including such a touch panel.
The touch panel of the present invention is constructed as follows. At least one of the resistor films of the upper and lower substrates has a comb shape composed of a plurality of resistive lines and a common connector. The coordinate values of the input point are detected from a one-dimensional resistance value.
Using such a touch panel, the liquid crystal display device of the present invention permits highly reliable detection of a screen input.
Typical constructions according to the present invention are summarized as follows.
(1) A touch panel of the present invention includes an upper substrate in the form of a soft film having an upper resistor film and a lower substrate in the form of a hard plate having a lower resistor film, the upper substrate and the lower substrate being bonded together so as to face each other, the touch panel providing a detection output representing a contact position between the upper resistor film and the lower resistor film as two-dimensional coordinate values,
wherein both the upper resistor film and the lower resistor film are of a comb shape having a plurality of resistive lines with a common connector at one end, and the resistive lines of the upper resistor film and the resistive lines of the lower resistor film extend so as to intersect each other.
(2) In the construction (1), a lower resistor film connector or an upper resistor film connector is formed on the upper substrate or the lower substrate for electrically connecting with the corresponding common connector of the other substrate.
With the above constructions, information on an input point can be uniquely detected from the x-coordinate value and the y-coordinate value on the touch panel. In addition, the resistance value of the resistor film of each substrate can be managed via the common connector of the substrate. This facilitates correction of a change in linearity and prevents the occurrence of an input error and a detection failure.
(3) Another touch panel of the present invention includes an upper substrate in the form of a soft film having an upper resistor film and a lower substrate in the form of a hard plate having a lower resistor film, the upper substrate and the lower substrate being bonded together so as to face each other, the touch panel providing a detection output representing a contact position between the upper resistor film and the lower resistor film as two-dimensional coordinate values,
wherein either the upper resistor film or the lower resistor film is-of a comb shape having a plurality of resistive lines with a common connector at one end, and the other resistor film is formed on the inner surface of one of the upper and lower substrate and at least on an entire information input area.
(4) In the construction (3), a resistor film connector is formed on the substrate which the comb shape resistor film is formed for electrically connecting with the resistor film of the other substrate.
With the constructions of (3) and (4) above, information on an input point can be uniquely determined from just one of the coordinate values, x or y, on the touch panel. In addition, the resistance value of the resistor film of one substrate can be managed via the common connector of the substrate. This facilitates correction of a change in linearity and prevents the occurrence of an input error and detection failure as in the constructions of (1) and (2) above.
In the constructions (1) to (4), the resistance value of the comb shape resistor film can be managed via a common connector. This allows for precise and reliable management of the resistance value over the entire resistor film. Moreover, by coating the common connector with a protection film made of an insulating material, deterioration in resistance characteristics due to the entry of moisture is minimized.
(5) A liquid crystal display device of the present invention includes: a liquid crystal panel including a liquid crystal layer sandwiched between a pair of substrates; and a touch panel formed on the display plane side of the liquid crystal panel,
the touch panel including an upper substrate consisting of a soft film having an upper resistor film, and a tower substrate consisting of a hard plate having a lower resistor film, the upper substrate and the lower substrate being bonded together so as to face each other, the touch panel providing a detection output representing a contact position between the upper resistor film and the lower resistor film as two-dimensional coordinate values,
wherein both the upper resistor film and the lower resistor film are of a comb shape having a plurality of resistive lines with a common connector at one end, and the resistive lines of the upper resistor film and the resistive lines of the lower resistor film extend so as to intersect each other.
With the above construction, information on an input point can be uniquely detected from the x-coordinate value and the y-coordinate value on the touch panel. In addition, the resistance value of the resistor film of each substrate can be managed via the common connector of the substrate. This facilitates correction of a change in linearity and prevents the occurrence of an input error and detection failure. The resultant liquid crystal display device exhibits improved reliability in screen input.
(6) In the construction (5), a resistor film connector is formed on either the upper substrate or the lower substrate for electrically connecting with the common connector of the other substrate.
(7) Another liquid crystal display device of the present invention includes: a liquid crystal panel including a liquid crystal layer sandwiched between a pair of substrates; and a touch panel formed on a display plane side of the liquid crystal panel,
the touch panel including an upper substrate consisting of a soft film having an upper resistor film and a lower substrate consisting of a hard plate having a lower resistor film, the upper substrate and the lower substrate being bonded together so as to face each other, the touch panel providing a detection output representing a contact position between the upper resistor film and the lower resistor film as two-dimensional coordinate values,
wherein either the upper resistor film and the lower resistor film is of a comb shape having a plurality of resistive lines with a common connector at one end, and the other resistor film covers the resistor film of comb shape.
(8) In the construction (6), a resistor film connector is formed on the substrate on which the comb shape resistor film is formed for electrically connecting with the resistor film of the other substrate.
(9) In the constructions (5), (6), (7), and (8), an auxiliary illuminator is interposed between the liquid crystal panel and the touch panel.
(10) In the constructions (5), (6), (7), and (8), an auxiliary illuminator is placed on the back of the liquid crystal panel.
(11) A protection film is formed to coat the common connector of the touch panel of the constructions (1) through (4) and of the touch panel incorporated in the liquid crystal display device of the constructions (5) through (10).
The protection film may be made of a known insulating material or adhesive material, such as an epoxy resin or a silicone resin. The protection of the common connector with such a protection film minimizes changes in resistance at the common connector. Therefore, by managing the resistance value of the comb shape resistor film in the input region via the common connector, resistance value management is facilitated and ensured. As a result, a highly reliable touch panel and a liquid crystal display device including such a touch panel are obtained.
The liquid crystal panel used in the liquid crystal display device of the present invention may be of a simple matrix type, an active matrix type, or any other known type. It should also be noted that the present invention is applicable, not only to a reflection type, but also to a transmission type liquid crystal display device.
The present invention is not limited to the constructions described above, but many modifications and variations may be made without departing from the technical principles of the present invention.